Electronic packages of the type described above, and particularly those which are especially adapted for use in information handling systems (computers), are well known in the art. Typically, these packages include some type of substrate (e.g., ceramic or fiberglass-reinforced epoxy) with the semiconductor chip electrically coupled thereto. The usual forms of such coupling are wirebonding (a plurality of gold wires interconnect contact sites on the chip to respective conductors on the substrate), thermocompression bonding (where heat and pressure is applied to bond two elements, e.g., projecting leads from a thin film flexible circuit and the respective chip contact sites, to thereby form an interdiffusion bond between these elements along a common interface) and soldering (wherein solder elements, e.g., spherical balls, are used to couple the chip's contact sites directly to the substrate's conductors or to leads on an interim thin film flexible circuit which is then electrically coupled to the substrate).
It is, of course, a key objective of all electronic package manufacturers to produce smaller and smaller (higher density) packages which are still capable of increased capacity over previous structures. At least two concerns arise when attempting such miniaturization, particularly when considering that increased operational demands on such devices as semiconductor chips results in such chips operating at greater and greater temperatures. To prevent package breakdown as a result of possible chip failure, providing adequate, effective heat sinking for the chip is absolutely necessary. A second concern involves circuit density and particularly the ability to increase such density and yet provide effective connections between all of the conductors (substrate and chip) which form part of the package's electrical circuitry.
In the manufacture of electronic packages, one known and accepted process used to provide the metallic portions which will eventually form part of the electrical circuitry is sputtering, wherein ions from a plasma bombard a "source", e.g., copper plate, such that atoms removed from the source are deposited onto the substrate base material, e.g., a thin polyimide layer located on a ceramic base. Often, an interim metal, e.g., chromium, is initially deposited, with the sputtered copper then deposited thereon. This chromium, designed primarily for providing increased adhesion of the copper, is also preferably sputtered. A second layer of chromium may also be deposited onto the deposited copper, also preferably using a sputtering operation. Sputtering is particularly desirable as a manufacturing process for forming electrical circuitry because of the ability to form extremely thin, uniform lines and pads of high density. By the term high density as used herein is understood to mean, with respect to circuit lines, the number of lines on the substrate's surface per linear inch, and, with respect to conductor pads or sites, the respective diameters or widths of the pads and the center-to center spacing between such pads.
As is known, sputtering results in the generation of relatively large amounts of heat from the base member receiving the sputtered atoms should the sputtering process be utilized at mass production rates demanded in today's computer field. Accordingly, the substrate material must be capable of withstanding such temperatures. Acceptable materials for such substrates have included, primarily, ceramics and the like, whereas materials such as fiberglass-reinforced epoxies (also known in the industry as FR4) are not considered acceptable due to the inability thereof to accept such increased temperatures, e.g., sometimes in excess of 400.degree. Celsius (C.), at typical mass production rates. Sputtering is an accepted process in the production of known packages using a ceramic substrate with a thin polyimide layer thereon (a thin layer of polyimide is capable of withstanding high production temperatures) and the circuitry formed on the polyimide, the resulting packages known as multilayered ceramic packages (MCPs).
Various electronic packages are illustrated in the following U.S. Pat. Nos.: U.S. Pat. No. 4,396,936 (McIver et al); U.S. Pat. No. 4,574,330 (Cohen et al); U.S. Pat. No. 4,941,067 (Craft); U.S. Pat. No. 5,019,941 (Craft); U.S. Pat. No. 5,280,409 (Selna et al); and U.S. Pat. No. 5,285,352 (Pastore et al). Such packages are also illustrated in the following International Business Machine's Technical Disclosure Bulletin (TDB) articles: (1) vol. 19, no. 11, April 1977 at pages 4165 and 4166; (2) vol. 31, no. 6, November 1988 at pages 372 and 373; and (3) vol. 34, no. 4B, September, 1991 at pages 408 and 409. Attention is also directed to German Offenlegungsschrift DE 31 15017 (November 1982). The packages as described in these publications, however, do not appear to adequately address the provision of high density circuitry on a base substrate other than ceramic or the like inorganic materials in which effective heat removal (sinking) is assured. Most particularly, none appear to teach such packages wherein the circuitry may be formed using a high temperature operation such as sputtering. Still further, none appear to teach use of a substrate comprised of a material having a coefficient of thermal expansion (CTE) that approximates that of the circuit member, e.g., printed circuit board (PCB), on which the substrate is positioned. Provision of both substrate and PCB with substantially similar CTEs significantly reduces stresses that may occur at the interface between these two members resulting from application of heat to the interface (e.g., to effect solder reflow). Understandably, significantly different rates of expansion at this location of the package could damage solder or similar type connections, and possibly render the package inoperative.
It is believed that an electronic package and process for producing same wherein the package provides effective heat removal and also possesses high density circuitry would constitute a significant advancement in the art. It is further believed that such an advancement would be forthcoming if such a process can be taught which is readily adaptable to mass production to thereby result in a finished end product which is relatively inexpensive in comparison to many known products of this type.